1. Field of the Invention
The present invention relates to a light-emitting diode chip component and to a light-emitting device fitted with such a light-emitting diode chip component.
2. Description of the Prior Art
Conventionally, two-color LED (light-emitting diode) chip components are widely used that are formed by placing two LED elements on a substrate so that it can emit light in two colors. FIG. 10A shows an example of such a two-color LED chip component. FIG. 10A is a perspective view of a small-sized LED chip component 109 for surface-mounting as seen obliquely from above. In FIG. 10A, numeral 1 represents an insulating substrate made of a heat-resistant material; numerals 2a and 2b represent LED elements; numeral 3 represents wires made of metal such as gold or aluminum for wire-bonding; numerals 4a, 4b, 4'a, and 4'b represent patterns of metal formed on the top surface of the insulating substrate 1; numeral 5 represents concave-surfaced cuts formed in four corners of the insulating substrate 1; numeral 6 represents a resin molding, which is indicated by broken lines, for protecting the LED elements 2a and 2b and other elements. The cuts 5 have their surfaces coated with metal extending from the top surface of the insulating substrate 1 to the bottom surface thereof so that they serve as terminals.
As shown in FIG. 10A, the two LED elements 2a and 2b are individually fixed near the center of the top surface of the insulating substrate 1 by die-bonding. The LED elements 2a and 2b have one end connected directly to the land of the patterns 4a and 4b, respectively, with silver paste or the like so as to form electrodes, and have the other end connected through wires 3 to the patterns 4'a and 4'b, respectively, by wire-bonding so as to form electrodes. The patterns 4a, 4b, 4'a, and 4'b each extend toward one of the four corners of the insulating substrate 1 so as to be connected to one of the cuts 5 that serve as terminals. The LED elements 2a and 2b and the wires 3 are sealed in and thereby protected by the resin molding 6.
In the actual manufacturing process, a plurality of units each constructed as shown in FIG. 10A are arranged on a single insulating substrate 1, and thereafter the individual LED chip components 109 are separated from one another by dicing. Meanwhile, the cuts 5 are formed by dividing through holes that have been formed in advance each into four parts. When an LED chip component 109 is mounted on a printed circuit board, it is soldered onto the printed circuit board by reflow soldering, using the cuts 5 as terminals. This requires the LED chip component 109 to be sufficiently heat-resistant, and therefore its insulating substrate 1 is made, for example, of BT (bismaleimide-triazine) resin or a special type of glass-epoxy resin that is highly heat-resistant.
The LED chip component 109 contains a circuit provided with four terminals as shown in FIG. 11. By turning on the LED elements 2a and 2b simultaneously or individually, it is possible to emit light in three colors in total. For example, in a combination where the LEDs 2a and 2b emit red and green light, respectively, they, when turned on simultaneously, provide orange light. The light is emitted principally in a direction normal to the top surface of the insulating substrate 1; that is, in FIG. 10A, the light is emitted upward, achieving so-called top-surface light emission.
In recent years, as portable phones, portable transceivers, and similar appliances become more and more popular, slimness has been eagerly sought in those appliances. As a result, also with LEDs that are widely used for displaying and illumination purposes in such appliances, suitability for use in slim appliances has been eagerly sought. For this reason, to minimize the effect of the size of LEDs on the thickness of appliances, such LEDs have been developed as achieve so-called side-surface light emission and can therefore be used to illuminate a display or the like from its sides. Thus, also in two-color LED chip components, side-surface light emission is highly desirable.
The easiest and surest way to achieve side-surface light emission is to mount an LED chip component vertically on a printed circuit board, that is, in such a way that a side surface of the insulating substrate on which LED elements are mounted faces the printed circuit board. However, as shown in FIG. 10B, the LED chip component 109 described above is so constructed that, when it is mounted vertically on a printed circuit board 10, whereas the patterns 4a and 4'a for the lower LED element 2a (not shown) can be soldered, the patterns 4b and 4'b for the upper LED element 2b (not shown) are situated away from the printed circuit board and therefore cannot be soldered. Accordingly, it has been customary to adopt this construction only in single-color LED chip components.
In recent years, miniaturization of LED chip components is eagerly sought. Miniaturizing LED chip components inevitable results in reducing the contact surface area between an insulating substrate and a resin molding, which in turn results in weakening the bond strength between them. As a result, the resin molding becomes more prone to come off the insulating substrate when it is subjected to an external mechanical force. In general, a resin molding exhibits a stronger bond strength against metal electrode patterns than against an insulating substrate. Accordingly, it is preferable to minimize the area of electrode patterns and thereby maximize the area in which the insulating substrate is exposed. However, in small LED chip components, it is impossible to reduce the area of electrode patterns beyond a certain limit.